Process of treating by-product zinc oxide



JAMES ELIGT BfiGGE- 9F WIIJMINGTGN, DELAWARE, ASSIGNOR TO E. L/DU FONT on NEMOURS & COMPANY, OF WILMINGTON, DELAWARE, A CORPORATION 02 DELAWARE.

PROCESS 01F TREATING BY-PRODUCT ZINC OKIDE.

insects.

Iqo Drawing.

To all whom it may concern:

Be it known that I, JAMEs Emo'r Booen, a citizen of the United States, and a resident of Wilmington, in the county of New Castle and State of Delaware, have invented a cer-.

a mixture containing zinc oxide contami nated with organic matter, solvents and certain inorganic impurities such as sodium hydroxide, carbonate, chloride, etc. Before such icy-product zinc oxide possesses an value for application for other purposes it must he freed from these impurities.

The present applicetion is directed toward such purification of this h'y-product zinc oxide as to maize it suitable for use as a substantially pure zinc oxide. For this purpose the various impurities must he to a great extent removed, the amounts remaining, if any, being such as to cause no inter ference in the utilization of the oxide.

-My invention may be illustrated by the following example As a first step in the purification, the byproduct zinc oxide is calcined at or below red heat, with or without agitatiomand in the presence of air, to volatilize or oxidize any organic material or unoxi'di'zed zinc which may be present. Residual solvent is of course vaporized, whereas non-volatile organic material is burned out in' this treatment. As a second step the calcined zinc oxide, preferably in a. finely subdivided state, is washed thoroughly with water. Such washing may be accomplished in a classifier of icnown'construction or by a batch process in suitable tanks by means of successive agitation and decantation. The extent of such treatment should be regulated by tests of the wash water for soluble salts and the treatment continued until no appreciable amount oi soluble salts, such as hydroxide, and chloride oi sodium, are being leached out. Afiec'each change of water the zinc oxide. is

Specification of Letters Patent.

Patented rtugufozl, limit.

Application filed October 21, 1920. Serial No. 418,391.

well agitated, after which settling is allowed to take place.

With some types of by-product nine oxide,

rapid settling does not occur. The material remains in suspension almost indefinitely, presumably due to assumption of a more or less colloidal state, with adsorption of the ions of'the soluble salts still present. This diiiicultyc'anbe overcome, however, by addition to the wash water of a very small amount of sulphuric acid. In this Way the colloidal suspension is coagulated and the ,is soluble'in a low-boiling organic solvent such as petroleum ether or ethyl alcohol, the crude lay-product me; he treated with such a solvent to remove tic'organic matter, the solvent being recovered later by distillation.

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After the removal of the organic matterv it is not always necessary to remove impurities such as soluble salts which may be present, since for some applications of zinc oxide these impurities may remain without lowering the value of the material.

In general my invention comprises the treatment of byproduct zinc oxide, and especially the zinc compound resulting from the use of zinc dust as a reducing agentin organic chemical reactions, to effect the removal of harmful impurities to such an ex tent that there will remain with the zinc oxide less than 1% of such impurities.

I claim 1. The process which comprises calcining by product zinc oxide, thereby forming a product containing water-solublev compounds, and washing the calcined product with Water to remove said soluble salts.

2. The process which comprises calcining by-product zinc oxide containing organic matter to volatilize the latter, and then washing the calcined product until the amount of impurities being leached out is no longer appreciable.

W "enmving: The process Whisk cam; 10 Wilde organic matter from Ery -91m ag the contaminated therewifll, mix

0 remove ide W 1 31 waterio mat a lms W 1011 may be: cumpolmds presem addzn 

